1. Field of the Invention
The present invention relates to an integrated circuit device. More specifically, the invention relates to a semiconductor integrated circuit having an error checking and correcting (ECC) function within a single chip or on a single printed circuit board and an integrated circuit system having the same function.
2. Description of the Related Art
As the semiconductor circuit components (semiconductor chips) of a semiconductor integrated circuit have decreased in size, soft errors have recently been caused. It is considered that the soft errors are caused by alpha rays emitted from an isotope in a package and neutrons coming from space. In particular, data in a memory chip appears here and there and thus becomes a problem. In the near future, soft errors will increase with the decrease of electric capacity of a cell node due to the miniaturization of memory chips.
Conventionally an ECC circuit system is used as one measure using a circuit against soft errors. If the ECC circuit system is adopted, a package has to incorporate a peripheral circuit chip for ECC and an ECC code storing memory chip as well as a data storing memory chip. In a semiconductor integrated circuit having a small-capacity memory chip (small-sized memory), however, the area share of the small-sized memory, which is held by the ECC code storing memory chip, is large, as is the area share held by the peripheral circuit chip for ECC. The ECC circuit system is therefore a major factor in increasing the costs of the semiconductor integrated circuit.
On the other hand, a large-scale integrated circuit system such as a silicon-on-chip (SoC) can be implemented at the present time. For example, in a static random access memory (SRAM) including a plurality of small-capacity RAMs, the memory macro capacity (total bit number) of the RAMs is as enormous as several megabits (Mb). The area share of the large-scale integrated circuit system, which is held by a memory chip itself, is large. If a conventional ECC circuit system is applied to the large-scale integrated circuit system, the area of the ECC circuit system leads to the increase of the area of a mounting substrate (printed circuit board). In other words, there is a problem that the ECC circuit system becomes a factor in increasing the costs of the integrated circuit system.
As related art, there has been proposed a technique of preventing the increase of the area of a mounting substrate due to the equipment of an ECC function (see Jpn. Pat. Appln. KOKAI Publication No. 2001-249854, for example). This proposal however aims at reducing the overhead of a memory chip by distributing a fixed number of ECC bits to two or more memory units of the memory chip.